1. Field of the Invention
This invention relates to a semiconductor light emitting device and methods of manufacturing it, and more precisely to a semiconductor light emitting device which gives a pure green light emission at a high brightness and methods of manufacturing it.
2. The Prior Art
Semiconductor light emitting devices, such as light emitting diodes, are obtained by growing a plurality of semiconductor layers on the front surface of a semiconductor substrate to fabricate a multi-layer semiconductor structure with a p-n junction(s) and then cutting it into an element(s). Among them, green light emitting semiconductor devices are obtained by forming one or more layers of both n-type and p-type GaP one after another on an n-type GaP single crystal substrate and cutting it into elements for practical use.
However, since GaP has an indirect transition-type band structure, the light emission efficiency is not sufficient even if the p-n junction(s) is formed, resulting in a light emitting device with a very low brightness. Because of this, the incorporation of isoelectronic traps which function as light emitting centers is performed as an effective means to improve the light emitting efficiency. For example, nitrogen (N) is doped to the GaP layer(s) near the p-n junction to substitute P sites in order to improve the light emitting efficiency. A GaP-type light emitting device thus doped with nitrogen emits a yellowish-green light with a peak wavelength of approximately 567 nm.
Research of GaP semiconductor light emitting devices has a long history, and the light emitting efficiency of the GaP semiconductor light emitting devices has been improved to the limit of the material property. However, it has been a problem that a sufficient light emitting efficiency could not be achieved because, as mentioned above, GaP essentially had an indirect transition-type band structure. Although the nitrogen doped GaP-type light emitting devices improved the light emitting efficiency, since the energy level of nitrogen was formed within the GaP band gap, it has been a problem that the light emitting wavelength became longer and the color changed to yellowish-green, and thus a pure green light could not be obtained.